In recent years, several studies have been conducted on the use of metallic ruthenium or ruthenium oxide as a material for a thin film electrode of a semiconductor device such as a DRAM due to their excellent electrical properties such as a specific resistance value. Metallic ruthenium, in particular, has better electrical properties than ruthenium oxide, and therefore is a desirable material for a thin film electrode of a semiconductor device. These ruthenium-containing thin films are most commonly formed by a CVD method, for example, because the CVD method can easily give a uniform thin film. Therefore, there is a need for a raw material compound suitable for the formation of a ruthenium-containing thin film by a CVD method.
A ruthenium complex having a β-diketonato or cyclopentadienyl derivative as a ligand, for example, is beginning to be widely used as a material for forming a thin film containing a ruthenium atom by a CVD method. The ruthenium complex having the above-mentioned ligand has good stability and sublimability, and therefore is useful as a ruthenium source for the CVD method.
Specifically, there has been disclosed a method for producing a mixed film of a metallic ruthenium thin film and a ruthenium oxide thin film, i.e. a film comprising a metallic ruthenium phase and a ruthenium oxide phase, by a CV) method, by reacting a β-diketonato ruthenium complex having a diene compound as a ligand with a β-diketonato ligand (see Non-Patent Document 1, for example. Incidentally, some of these complexes are known compounds, but are solid at ordinary temperature.) with an oxygen gas at a high temperature (see Patent Document 1 and Non-Patent Document 2, for example.). In this method, however, owing to the use of the oxygen gas, the mixing of ruthenium oxide, which has a much higher specific resistance value than metallic ruthenium, may be inevitable. In addition, owing to the high film-forming temperature, an impurity atom such as a carbon atom or the like may be mixed into the obtained ruthenium thin film, leading to the reduction of the specific resistance value.
There has been also disclosed a method for producing a metallic ruthenium thin film by a CVD method, by reacting a ruthenium complex having a β-diketonato and a carbonyl as a ligand with hydrogen at a high temperature (see Patent Document 2, for example.). According to this method, however, ruthenium oxide may be mixed in the obtained ruthenium thin film, leading to the reduction of the specific resistance value, although a hydrogen gas is used. (The oxygen content in the obtained ruthenium thin film is 2 to 3%.)
Furthermore, Patent Document 3 discloses a ruthenium complex comprising a β-diketonato having an alkoxyalkylmethyl group as a ligand, as a material for forming a thin film by a CVD method. None of the ruthenium complexes disclosed herein has a diene compound as a ligand.